Parkinson's disease, like Alzheimer's disease may be genetically heterogenous. We will determine whether genetic influences are greater in families of probands with early onset PD (< or = 50 years) compared to late onset PD (>50 years) and tremor dominant PD compared to postural instability gait disorder PD. We will study 300 PD patients from the community and 300 community controls and 400 service-based PD cases and 400 random controls and all first degree relatives. Segregation analysis will be performed to determine the optimal strategy for a future genetic linkage study.